Field of the Invention
The present invention relates to a post-processing device that accumulates sheets fed from an image forming device and performs post-processing for the accumulated sheets and to a post-processing mechanism capable of performing the post-processing without delaying an image forming process performed upstream of the post-processing device.
Description of the Related Art
In general, a system of such a type uses an image forming device provided at an upstream side to form an image on sheets and then uses a post-processing device provided at a downstream side to accumulate the image-formed sheets into a set and to perform bookbinding and other post-processing. Such a system is required, in terms of system operating efficiency, to continuously form an image by means of the upstream side image forming device and to perform the post-processing at the downstream side in accordance with a processing speed of the image forming device.
Thus, in order to meet the above requirement, a conveying system is adopted, in which a succeeding sheet that has been subjected to image formation in an upstream side device and fed therefrom during execution of post-processing such as bookbinding performed for preceding sheets accumulated and aligned in the post-processing device is made to temporarily stay in the middle of a conveying path and then fed to the post-processing device after completion of the post-processing operation.
For example, Japanese Patent No. 5,248,785 (Patent Document 1) discloses a post-processing device provided with a straight path that guides a sheet fed from an image forming device to a first processing section and a switchback path that is branched from the straight path and guides the sheet to a second processing section. This publication proposes a path configuration where a succeeding sheet fed from an upstream side while the first processing section performs a processing operation is made to stay in the switchback path for guiding a sheet to the second processing section and a succeeding sheet fed from the upstream side while the second processing section performs a processing operation is made to stay in the straight path.
An image forming device provided upstream of the above post-processing device is configured to form an image on a sheet at a predetermined timing irrespective of the downstream side post-processing operation and discharges the image-formed sheet from a sheet discharge port. The post-processing device receives the discharged sheet and makes the received sheet stay in the switchback path for guiding a sheet to the second processing section when a post-processing mode specifies the first processing section, while makes the received sheet stay in the straight path for guiding a sheet to the first processing section when the post-processing mode specifies the second processing section. Then, after completion of a current job in the first or second processing section, the staying sheet is fed to the first or second processing for subsequent processing.